Re: [PATCH v5 05/11] drm: nova: Add an info ioctl

[Danilo Krummrich]

On Fri Sep 4, 2026 at 9:49 AM CEST, Alistair Popple wrote:
> On 2026-09-03 at 20:42 +1000, Danilo Krummrich <dakr@xxxxxxxxxx> wrote...
>> I think there never was a "rather than". The point was that if userspace has
>> conditionals based on the architecture it shouldn't have to figure it out based
>> on the chipid, as this has been done by the kernel already.
>
> I see. Maybe that was a bad assumption on my behalf, because I assumed that if
> you make a precise hardware description available (chip-id) there'd be no point
> making an imprecise subset of that description (arch) available as it isn't
> particularly useful if you can't use it in isolation for any generic purpose.

Except that it is used in isolation for a generic purpose e.g. in NAK.

>> Then in NAK (src/nouveau/compiler/nak/ir.rs), there's this code.
>> 
>> 	fn is_turing(&self) -> bool {
>> 	    self.sm() >= 73 && self.sm() < 80
>> 	}
>> 	
>> 	fn is_ampere(&self) -> bool {
>> 	    self.sm() >= 80 && self.sm() < 89
>> 	}
>> 	
>> 	fn is_ada(&self) -> bool {
>> 	    self.sm() == 89
>> 	}
>> 	
>> 	#[allow(dead_code)]
>> 	fn is_hopper(&self) -> bool {
>> 	    self.sm() >= 90 && self.sm() < 100
>> 	}
>> 	
>> 	fn is_blackwell_a(&self) -> bool {
>> 	    self.sm() >= 100 && self.sm() < 110
>> 	}
>> 	
>> 	fn is_blackwell_b(&self) -> bool {
>> 	    self.sm() >= 120 && self.sm() < 130
>> 	}
>> 	
>> 	fn is_blackwell(&self) -> bool {
>> 	    self.is_blackwell_a() || self.is_blackwell_b()
>> 	}
>> 
>> That's two unnecessary indirections for something the kernel already has
>> available.
>
> Again though is what the kernel provides in the form of an arch actually useful
> to user-space? Obviously the code above makes it look nice and simple like that,
> but as I have been saying more complete implementations can't just rely on arch
> alone and so are still going to have lookup tables both for SM and for other
> info the kernel can't provide.

Are you saying that NAK oversimplifies things and hence gets away with per
architecture checks in src/nouveau/compiler/nak/sm70.rs? And that a "more
complete implementation" would be specialized to a point where it becomes
impossible to have any common code per architecture and in general?